On Wednesday, Facebook introduced a new location-based service that allows users to share their location with friends. With more than 500 million members, Facebook is now the third-most-popular video site on the Web according to comScore, trailing only Google (Nasdaq: GOOG) and Yahoo!.

Earlier in the week, Motley Fool Money Radio Show host Chris Hill talked about the business of Facebook with David Kirkpatrick, author of The Facebook Effect: The Inside Story of the Company That Is Connecting the World. In this excerpt, David Kirkpatrick talks about Apple's (Nasdaq: AAPL) importance to the future of Facebook.

Chris Hill: You write that Zuckerberg has been spending an increasing amount of time with Steve Jobs, who is someone that he admires. You've written about Apple and Steve Jobs before. Are there parallels that you see between Jobs and Zuckerberg?

David Kirkpatrick: Well, there are parallels in terms of the scope of their vision, and in the obsessiveness of their commitment to their companies. I think obviously, Zuckerberg admires Jobs tremendously. Ironically, Steve Jobs does not seem to be that interested in social stuff, to the degree that almost anybody else in the industry is. Apple has historically and consistently been among the least social of major technology companies, which is interesting, considering that we think we live in a social age. Yet Apple is the computer company, the technology company, with the highest market cap. It's sort of an odd, disjunctive fact that is worth meditating upon.

But I will tell you something they do have in common that is very important. The Facebook application is by far the most important application on both the iPhone and the iPad. Without the Facebook application, my own opinion is the iPhone would never have become as important as it is. It's the single most widely used application. It's so heavily used compared to other apps that I have been told by someone who thought he knew the data -- this is highly secret data and I don't know the actual numbers -- that more than half of all usage of the iPhone of apps, other than those provided by the phone itself like telephony and email, is coming from Facebook. And on the iPad, too, it's just a huge, huge part of usage. So in a way, Apple and Facebook are joined at the hip, and I think that's one reason why Zuckerberg and Jobs have been spending time together.

Hill: I want to ask you one more question about Mark Zuckerberg. There have been a lot of stories about Zuckerberg stepping on a lot of toes. I'm quoting from the San Francisco Chronicle review of your book: "Zuckerberg comes across as a reclusive know-it-all, an irascible rebel prone to sophomoric pranks." One of the things we think about at The Motley Fool when we think about CEOs is, how well does this person know themselves, and as a business leader, have they set up systems around them to compensate for their own weaknesses? Does Zuckerberg strike you as a guy who knows what his weaknesses are, and has he set up systems in place to deal with them?

Kirkpatrick:   For the most part, he probably should be the paragon for that kind of a measurement of anybody else. He's done an extraordinary job surrounding himself with people who have talents that either he doesn't have, or that he isn't interested in, but that are critical jobs to be done ... I would say even though Facebook was started when Mark Zuckerberg was a sophomore at Harvard, he is the least sophomoric 26-year-old on the planet. This guy is 26 years old; he's got a $1.5 billion revenue business with 500 million customers. No 26-year-old in human history has ever had a business success comparable to that, and that includes Bill Gates at that age.

So let's face it, this guy is uniquely successful. This is one reason why I felt I had to write the book. I honestly think that Facebook is probably the single most impactful business phenomenon of our era, and that's why I felt it was almost an obligation to write this book, since I had this sort of unique access and ability to do it. And my admiration for Zuckerberg is quite extreme.

Yes, there are stories about him being unfair to early partners, and people that he worked for or supposedly took ideas from, and I think there may be some truth to some of those rumors. I think he did probably make some stupid mistakes when he was 19 years old and getting this thing started. I don't think he is fundamentally an unethical person. I think he is a very ethical person who is very, very focused on a very, very big-picture set of goals.

Want to read more on the business of Facebook? Fool contributor Rich Smith disagrees with one Wall Street analyst who thinks Facebook will eat Google's lunch.